Update RELEASE_NOTES.md for 1.5.52 release

[Aaronontheweb]

Summary

Prepare for the 1.5.52 release by updating RELEASE_NOTES.md and Directory.Build.props with the latest version and release notes.

Changes

• Updated version to 1.5.52 (dated October 9th, 2025)
• Added release notes for API deprecation and Akka.NET version bump
• Updated Directory.Build.props metadata

Release Notes

API Changes

• Deprecate JournalOptions.Adapters property in favor of callback API (Deprecate JournalOptions.Adapters property in favor of callback API #669) - resolves Deprecate JournalOptions.Adapters property in favor of unified callback API #665

Updates

• Bump Akka version from 1.5.51 to 1.5.52

Test plan

• Build completes successfully
• All tests pass
• Version metadata is correct in Directory.Build.props